Implant and follow-up data
For all included leads, sensing, and pacing threshold, and impedance were recorded at discharge time and their regular follow-up. Sensing and pacing thresholds were calculated for a pulse duration of 0.4 milliseconds. At follow-up time, failure of a lead and its reason also were recorded. The reason for failure was either primary or secondary. Primary reasons for failure included replacement due to unacceptable high pacing threshold and sensing abnormality, lead fracture, loss of capture, and lead displacement. Secondary ones consisted of infection of the generator pocket and accidentally lead damage during heart surgery. The lead survival time (duration of being functional) was calculated as the interval between lead implantation and the time that failure was observed in the clinical follow-up. When a failure occurred, and a lead was exchanged, the new lead enrolled in the study and the patient characteristics (demographics, electrocardiographic and echocardiographic features) at the time of lead implantation were enrolled.